The present invention relates to the field of radio frequency antennas. More particularly, but without limitation thereto, the present invention is directed to a high-power broadband antenna.
The incorporation of RLC (resistor-inductor-capacitor) electrical networks into a whip antenna structure to maintain an acceptably low voltage standing wave ratio (VSWR) with increased frequency bandwidth is well known. A single whip antenna using this technique is described by B. Halpern and R. Mittra, RM Associates, Champaign, Ill. in "A Study of Whip Antennas for Use in Broadband Communications Systems" prepared for Naval Electronics Systems Command, Washington, D.C., February 1986. The antennas in this study were single whip antennas, and did not cover the entire HF band of 2-30 MHz with a VSWR of less than about 3:1. Further research at the Naval Command, Control, and Ocean Surveillance Center in San Diego, Calif. established that a single whip antenna can be made to cover the entire HF band by incorporating two RLC electrical networks having appropriate component values and located between antenna elements having appropriate lengths. This technique is referred to as "electrical loading". A problem with this technique is that at lengths of about 12 meters the radiation efficiency falls below 10 percent under 4 MHz, and below 2 percent under 3 MHz. The average radiation efficiency between 6-30 MHz would only be about 45 percent. With currently available resistors, such an antenna can accept a maximum RF power input of only about 1-2 kW.
A need thus exists to increase the power handling capability of HF antennas in the range of 2-30 MHz, and to improve overall antenna efficiency over the broadband frequency range. The present invention is directed to these needs and may provide further related advantages.